The force of the water had churned up a thick blanket of foam over the river and all three disappeared into the foam. The foam is six feet deep in areas.

"It's just such a hectic environment," Sioux Falls Fire Rescue Cpt. Nick Luther told ABCNews.com. "The water moves so fast. The temperature, the ice, the foam, there are so many obstacles."

Firefighters used blowers to try and reduce the amount of foam and a backhoe was brought in to break through the ice, KSFY reported. Once some of the ice was removed, the divers went into the water today.

"There's one area that [crews] are working around that is essentially 15 feet deep," Luther said.

Bystanders who witnessed the accident say they tried to help rescue the boy and the duo who jumped in to save him. One man was able to grab on to the unidentified man.

"We had him. There were three of us that had him and he had a kid with him, but he just slipped man, he just slipped," Napoleon Ducheneaus told KSFY.

"We happen to just be walking over the bridge and we noticed somebody was down there reaching in to the foam and we looked a little bit closer and we could see they were holding on to somebody, trying to pull him out," another bystander told KSFY.

"I feel hopeless. I wish there was something I could have done."

The boy "is doing just fine," and is with his mother, Luther said.

The 6-year-old suffered no injuries, but was taken to the hospital as a formality, he said.